This invention relates to illumination devices. More particularly, the invention relates to illuminating a large surface area or playing surface such as a sports or recreation field. The invention is also amenable to other applications including lighting parking lots, as well as other large areas including indoor areas.
Existing sports lighting installations normally comprise several poles and a multiplicity of similar fixtures that are typically the same wattage and model with different photometric characteristics. The fixtures are mounted on poles with cross-arms and individually aimed in such a way that the various photometric patterns fill in regions of the lighted area to meet the desired uniformity and light levels. In some applications this requires measuring the lighting results and pointing the fixtures at the time of installation to compensate for variations in the individual fixture photometry, photometric axis, and the inaccuracies of fixture pointing on the mounting arm and pole.
A typical parks and recreation sports field might incorporate four to eight poles and approximately 50-60 fixtures. The fixtures typically comprise several general purpose flood lights with National Electrical Manufacturers Association (“NEMA”) types describing the photometric characteristics of the fixtures. NEMA types 3×3 (med-narrow), 4×4, 5×5, and 6×6 (wide) would normally be used. Each fixture is installed on a cross-arm on a pole and aimed in both azimuth and elevation according to a design plan to create a composite field lighting pattern that meets uniformity and light level specifications. In general, each fixture lights a limited portion of the entire field that is substantially less than the area of the entire field. Lamp failures in individual fixtures cause local dimmed regions on the field and uniformity loss. Also, portions of the fixtures cannot be turned off to conserve energy without creating dimmed regions on the field. Furthermore, each fixture must be pointed or aimed individually at the time of installation to achieve the intended lighting result. This, of course, becomes a time consuming and expensive task.
FIG. 1 depicts a known lighting system where a plurality of floodlights A mount to a cross-arm B of a pole C. The floodlights generate generally elliptical distribution patterns D that illuminate separate portions of a playing surface E. Light poles and fixtures are added as necessary to illuminate the playing surface to the desired light level and uniformity. In general, the economics of purchase and operating costs drive the design to use the minimum number of fixtures necessary to meet the light level and uniformity requirements. This substantially limits or precludes redundancy in light coverage on the field and if one fixture fails, a region of low light level results in the area that was illuminated by the light emitted from the failed fixture.
Accordingly, it is desirable to provide a lighting system and method where if one fixture fails, the average light level over the entire playing surface or field is reduced, but the uniformity of the light on the field remains substantially the same. It is also desirable to provide a lighting system and method that reduces the complexity of installation of the system by greatly reducing or eliminating fixture aiming.